Irons are known which use the steam generated by themselves to facilitate ironing and basically comprise a tank in which water is stored to be supplied through a duct (at the time of ironing) to a vaporizing chamber that is located in the soleplate of the iron and is heated by electric resistors. In these irons there is no possibility of closing off passage through the duct nor, therefore, of regulating the quantity of steam in accordance with the needs of the garment to be ironed, but rather the duct is always open and water constantly flowing through and being vaporized in the vaporizing chamber.
Steam irons are also known which correct the problem indicated by disposing of a lock pin in the drip valve inserted in the water bypass to the vaporizing chamber.
These irons equipped with drip valve with lock pin, though improving on their predecessors, present the disadvantage that the passage of water to the vaporizing chamber, when the lock pin is in the proper position, occurs without the chamber having reached sufficient temperature and that results, at the beginning of ironing or because of the reduction of temperature due to ironing itself, in the discharge of unvaporized drops of water outside the iron, overly dampening the garment and making ironing difficult.
With a view to solving this problem, irons are known that dispose of a bimetallic element and a lock pin, the head of which, in normal operation of the iron, is permanently seated on the drip valve until the vaporizing chamber acquires sufficient temperature and the bimetallic element is excited and displaces the head of the pin from its seat to the extent corresponding to the position selected by an external regulating control. An iron of this type is that corresponding to U.S. Pat. No. 4,125,953.
The most important characteristic of this type of iron is that excitation of the bimetallic element is used directly to displace the lock pin from its permanent seat and as locking is ensured by the action of a resilient spring, this means that:
the lock pin must have a special configuration or be connected with the bimetallic element through some intermediate piece, so that the movement of the bimetallic element is converted into a pin opening displacement;
the bimetallic element has to possess special characteristics of mechanical strength, since stresses capable of overcoming the resistance of the resilient spring ensuring the seating of the lock pin are accomplished by the movement of the bimetallic element and bimetallic elements are not normally subjected to such stresses;
the resilient spring as well as the bimetallic element must be perfectly calibrated so that on different irons a given position of the regulating control will always correspond to the same degree of discharge of steam, for otherwise the quality of ironing and of the iron itself would be affected. This calibration also has to be such that it enables the bimetallic element to compress the spring in the opening, without impairing the pressure necessary for seating of the pin, which is also entrusted to the spring;
the end of the lock pin as well as the element on which it is seated suffer excessively due to the continuous reciprocal seatings that are necessary in this mode of operation.